Yggdrasil (Dungeons and Dragons)

Advanced Dungeons & Dragons 1st edition (1977-1988)

The first edition Manual of the Planes by Jeff Grubb describes Yggdrasil as an astral landmark, noting that it is normally encountered by travelers from worlds that worship the Norse mythoi, but travelers from other Prime Material worlds can encounter the tree. It is a long-standing conduit from the Outer Planes to alternate prime worlds that was created by a group of deities and worshippers in the Prime Material plane. Yggdrasil is the "World Ash" that links several outer planes to the Prime Material plane, in the Norse mythos. It runs from Gladsheim, home of most of the Norse mythos, to Nifflheim, the center layer of the three Glooms of Hades and the dwelling place of the goddess of the same name. Roots and branches of Yggdrasil wind through most of the Prime worlds where these deities are recognized. The tree is a solid and permanent conduit that weathers the waxing and waning of faiths in the Prime Material and the fortunes of gods in the outer planes. The traveler is confronted with a huge tree rising from the mist of the Astral and disappearing far into the distance. The traveler can then climb the tree to the appropriate outer plane, descend to the reachable lower planes, or explore the alternate Prime worlds that the conduits touch upon. At the true terminus, the tree ends in a color pool similar to that of a fixed portal. The traveler can then pass into the outer plane as if moving into an alternate Prime Material or the Astral plane. Yggdrasil and Mount Olympus are the best-known of the permanent conduits that link the outer planes with the Prime and with other nonlinear outer planes. Magical interplanar portals generally only appear in the top layer of the outer planes, although some free-standing portals that pass through the Astral, like the Yggdrasil, pierce the lower reaches of some planes. The Norse gods are bound together, both by the permanent portal of Yggdrasil and by the highly dangerous nature of the plane of Gladsheim itself. The realm of Asgard is a conglomeration of many smaller realms and domains of the various gods near the permanent multiplanar portal that is Yggdrasil, the World Ash. The plane of Gladsheim is the topmost point of Yggdrasil. The roots of this mighty tree lie in the second layer of the plane of Hades, and its branches touch every alternate Prime Material world where the Norse pantheon has been or is being worshipped. The World Ash is the home of many giant stags who browse upon its leaves, and it also contains numerous nests of giant eagles. A giant squirrel named Ratatosk scales the tree continuously, conveying threats to the eagle and others from the dragons of Niflheim. The apertures that the Yggdrasil causes in the Prime worlds are fixed and limited to those places where the Norse gods are known. Yggdrasil reaches the lower players of the plane of Hades. Niflheim is the second layer of Hades, the layer reached by the Yggdrasil in its course from Gladsheim. The main barrier between the layer of Oinos and Niflheim leads to the roots of the Yggdrasil, in full view of Hel's feast hall. The Yggdrasil (and the main barrier region from Oinos) decamps at the base of a low hill. At the base of the Yggdrasil is Nidhogg, a huge, very ancient red dragon, and that dragon's innumerable brood. Nidhogg's task is to gnaw at the roots of the World Ash and eventually cut the link from Niflheim to Asgard, but the ash sets down new roots even as Nidhogg consumes them. The Norns are said to have their well of souls at the very edge of the center of the plane of Concordant Opposition. They identify this area as an unattainable part of the Yggdrasil, though the behavior of this area is unlike that of any other part of the World Ash conduit.

Advanced Dungeons & Dragons 2nd edition (1989-1999)

The Planescape Campaign Setting (1994) boxed set by David "Zeb" Cook describes Yggdrasil in the booklet "A DM Guide to the Planes" as one of the paths between planes and layers. One feature of the planes is the great tree Yggdrasil, the World Ash. Rising on the first layer of Ysgard, Yggdrasil's roots and branches extend into many other planes, providing a way for travelers to get around. No one has mapped the extent of these pathways, but some of the important paths are known. One of the roots reaches to Niflheim on the Gray Waste, and another stretches to Pandemonium, where Loki of the Norse pantheon resides. The branches are no less widespread, even crossing the silvery void of the Astral Plane to reach the very Prime Material. There, the smallest branch tips touch hundreds of worlds where the Norse gods are revered or remembered. Other branches reach Elysium, the Beastlands, and Limbo, and there are likely to be many more such pathways. Traveling Yggdrasil's paths requires the traveler to climb through the branches or roots. At each planar crossing, the tree disappears through a portal of shimmering color, like a color pool found on the Astral. Only the vaguest of shapes can be seen through the window. To know for certain what lies on the other side, a traveler must step through. The colored portals are all two-way passages. Reaching into Niflheim, a layer of the Gray Waste, is a root of Yggdrasil, the World Ash. Curled around this root is a great wingless dragon Nidhogg, who forever gnaws at the root and will ultimately kill the tree. The highest level of the plane of Ysgard is where the top of Yggdrasil is located. As Yggdrasil stretches down to the Gray Waste, it extends branches and roots into various crystal spheres on the Prime Material where the Norse powers are worshipped. The booklet "Sigil and Beyond" mentions that on the plane of the Outlands, the Norns of Norse lore live among the roots of the plane-spanning Yggdrasil. The canopy is so thick that the realm's like a great cavern. In the gate town of Glorium on the plane of the Outlands, one of the gates to Ysgard is one of Yggdrasil's roots. This path is found in the mountains behind the town. There, characters will find the arching gap of a cave mouth, and somewhere inside the cavern is one of Yggdrasil's plane-spanning roots. There are many side passages, some of which lead to unpleasant places like Ilsensine's realm of Gzemnid's Maze.

The boxed set Planes of Chaos (1994) by Lester Smith and Wolfgang Baur notes in "The Book of Chaos" booklet that on the plane of Arborea, a root of Yggdrasil surfaces near the lower, darker end of the realm of Arvandor, near a settlement of ratarosk (self-appointed guardians of the World Ash) and elves. The root and settlement are both named the Gnarl. A large root of the World Ash Yggdrasil reaches into Pandemonium in Loki's realm, forming the center supporting beam of the roof of Winter's Hall. The plane of Ysgard's great highway is Yggdrasil, whose branches reach through the worlds and planes to every place where the Norse gods are worshipped. One major branch of Yggdrasil reaches to Niflheim, the "Abode of Darkness." Niflheim is a cold and harsh realm, the second layer of the Gray Wastes. A monstrous dog named Garm guards the cavern Gniper, where Helvig, the long and troublesome road to Niflheim, begins. Garm serves his mistress Hel and no other, and, though he allows anyone into NIflheim, he allows no one out. Other branches reach into the home of the Norns into the Outlands, into Loki's Winter's Hall in Pandemonium, into Arborea near the Gnarl in the realm of Arvandor, and into each of the spheres of the Prime plane where the Norse are worshipped. Within Ysgard, branches reach to Rowan's Hall (the headquarters of the faction known as the Fated), near the Well of Mimir in Jotunheim, under ground in Vanaheim near Smoke-top, and in dozens of other sites. Hundreds of the World Ash's lesser branches are hidden or private, and more branches are discovered frequently. Power keys, which help clerics cast their spells at full power, can be obtained by searching Yggdrasil, where the runes are carved deep under the bark near the World Ash's roots. The natives of Yggdrasil can be numbered among the creatures of Ysgard, since they have access to many sites on the plane through the World Ash. The most numerous of these are the ratatosk, a race of climbers who consider the World Ash their patron god. The Well of Urd on the Outlands is a magical spring that has its beginning from the ground in Asgard, where one of the major roots of Yggdrasil enters the land. In the realm of Jotunheim, the well of Mimir the Wise is sunk into a dark crevasse between two hills, where one of the major roots of Yggdrasil enters the land. Volund the Unruly, the Spear-shaker from Nidavellir is the greatest mage-smith of the realm of Vanaheim, and he lives underground near a root of Yggdrasil as far from the sea as one can get in Vanaheim, under a mountain called Smoke-Top. The booklet "The Travelogue" describes how deep within the plane of Limbo's ever-changing soup lies one bit of terrain that remains constant throughout time without the preserving attention of intelligent beings. Most commonly referred to as Pinwheel - due to its constant spin and the streamers of half-formed matter that cling to its edges - this location is the site at which the World Ash Yggdrasil connects to the plane. Most beings believe that the fact that Pinwheel is home to a branch of Yggdrasil is explanation enough for the island's existence, as Yggdrasil reaches into Limbo, and by virtue of its own stability, imposes stability on this locale, giving rise to the island. Others point out that Yggdrasil is not a thinking being, so it does not make sense for it to impose stability on Limbo's soup, but rather the branch of the World Ash drops into chaos matter without any local effect at all and suspect that Yggdrasil reaches here because Pinwheel is stable, rather than the other way around. Pinwheel is heavily forested, and the forest ranges from pine and fir near the site's raised center, where Yggdrasil can be found, to humid jungle at its edges. Like most islands, Pinwheel rises at its center to a mountainous peak, which is where the branch of Yggdrasil connects. Yggdrasil is a tree, but it is also a portal, a great highway between the planes. It is the home of the ratatosk, the squirrel-folk, who know every branch and portal of the great tree, even the root that is said to lead into the rafters of the Carpenter's Guildhall in Sigil. Yggdrasil is a silver-barked ash, a tree with shimmering blue-black, oval leaves and a very rough, flaking bark that resembles a plowed field of gray clay. The branches rise from Yggdrasil's trunk and are miles long, and not all of them have portals at the end, so long dead-end detours are common for groups traveling without a guide or directions. The World Ash is guarded by creatures that never leave its shade, creatures that live and die on its bark. Yggdrasil's eagles and the ratatosk are among them, and all along its length, Yggdrasil's bark and heartwood are home to enormous burrowing beetles, and its leaves and fungi feed entire herds of wild boar. The biggest and most terrible guardians are at the gates, where the roots and branches reach across the planar boundaries - for instance, at the World Ash's access to Niflheim. Called the land of mists, Niflheim is a layer of the Gray Waste that lies below Yggdrasil's roots and is guarded by the fell dragon Nidhogg. Besides Nidhogg, other guardians include aasimon in the upper branches, yugoloths in the lower ones, and Heimdall's petitioners near Ysgard. Many powerful beings want to control the entrances to their realms, but, because Yggdrasil's branches are often shifted by astral winds, the gates move from place to place, as a tree's branches sway and bend. Yggdrasil connects planes very quickly and directly, and few journeys on the World Ash take more than a week. However, traveling along the trunk has risks, including falls into the Astral and walking down the wrong branch to an unexpected plane. Gravity shifts along Yggdrasil's mountain-sized trunk. Along long sections gravity is simply toward the center of the trunk, but as a planar portal approaches, the great tree's gravity slowly matches local gravity.

A Player's Primer to the Outlands (1995) by Jeff Grubb notes that in the gate town of Ecstasy on the plane the Outlands, the city's gate takes people to the layer of Amoria on the plane of Elysium, on the banks of the river Oceanus.